In order to prepare lyophilized cells of Bifidobacterium bifidum TMC3115 with high viability, the impact of the initial pH of the medium, different carbon and nitrogen sources, and inoculum quantity on the viable cell count was studied by the one-factor-at-a-time method. Subsequently, an orthogonal array design was applied to optimize combinations of carbon and nitrogen sources based on the pH of the medium at 16 h of culture, cell density (expressed as optical density) and viable cell count. The efficacy of 18 cryoprotectants on the probiotic strain was investigated, and the optimization of cryoprotectant blends was carried out using an orthogonal array design. The results showed that when the initial medium pH was 7.2 and the inoculum amount was 4%, the viable cell count reached the highest. The optimized medium was composed of glucose 25 g/L, tryptone 20 g/L, yeast peptone 10 g/L, yeast extract FM902 15 g/L, diammonium citrate 2 g/L, anhydrous sodium acetate 5 g/L, dipotassium phosphate 2 g/L, Tween-80 1 g/L, magnesium sulfate 0.58 g/L, manganese sulfate 0.25 g/L, and L-cysteine hydrochloride 0.5 g/L. The optimal cryoprotectant was composed of skim milk 12%, trehalose 12%, glycerol 1.2%, sodium glutamate 0.6%, and L-cysteine hydrochloride 0.15%. The viable cell count of the freeze-dried culture produced under the optimized conditions reached 4.26 × 1011 CFU/g.

Using gas chromatography-tandem mass spectrometry (GC-MS), an indirect method was established for the simultaneous detection of 3-chloropropanol esters (3-MCPDE) and glycidyl esters (GE) in infant formula for special medical purposes. The conditions for sample extraction and transesterification/hydrolysis were optimized and stable isotope dilution was used to improve the accuracy and precision of the method. The results showed that the method exhibited good linearity in the range of 0.005–2.000 μg/mL (R2 ≥ 0.999), together with a limit of detection (LOD) of 5 μg/kg and a limit of quantification (LOQ) of 25 μg/kg (both calculated based on the corresponding amount of chloropropanol). The recoveries of the analytes spiked in infant formula for special medical purposes at 25, 125 and 250 μg/kg were 88.5%–104.1%, and the relative standard deviations (RSDs) for six replication determinations were less than 15% (n = 6). The levels of 3-MCPDE and GE in three types of commercial infant formula for special medical purposes were below the maximum limits set by the EU.

A probiotic lactic acid bacterium, named LC577, was isolated from Tibetan kefir. This bacterial strain was identified as Lactococcuslactis casei based on its morphologic properties, 16S rRNA sequence analysis and physiological and biochemical characteristics. The strain had a strong ability to produce acid, and produced a cheese-like aroma after fermentation in skim milk. In addition, it showed tolerance to acid and bile. After 4 h culture in a simulated gastric fluid, the viable count increased slightly, but decreased to 6.15 × 105 CFU/mL after exposed to 3 g/L oxgall for 4 h.

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of vancomycin, norvancomycin and teicoplanin in milk samples. Selective reaction monitoring was performed and the external standard method was used for quantification. Among various solvents tested, 0.1% formic acid-acetonitrile (85:15, V/V) was selected. Samples were ultrasonically extracted and vancomycin and norvancomycin were cleaned up by cation exchange column chromatography, while teicoplanin was purified using a C18 solid-phase extraction (SPE) cartridge. Acetonitrile-0.1% formic acid solution was chosen as mobile phase for gradient elution. The analytes were separated on a reversed-phase C18 column before being analyzed by mass spectrometry. The limits of detection (LOD) for vancomycin, norvancomycin and teicoplanin were 2, 1 and 2 μg/kg, and the limits of quantitation (LOQ) were 4, 2 and 4 μg/kg, respectively. The recoveries of the method ranged from 77.3% to 84.5% at spiked levels equal to LOQ, 5 × LOQ and 10 × LOQ, with relative standard deviations (RSD) of 4.7%–7.2%. The method could be used in the qualitative and quantitative detection of vancomycin, norvancomycin and teicoplanin in milk samples.

In this study, real-time quantitative polymerase chain reaction (q-PCR) was used to compare and quantitatively analyze the predominant species Lactobacillus helveticus, Leuconostoc mesenteroides and Lactococcus lactis subsp. lactis isolated from 28 samples of traditional fermented dairy products（including 7 samples of fermented sheep milk, 8 samples of fermented goat milk and 13 samples of fermented cow milk）from Ordos in Inner Mongolia. The results showed that the order of the number of three predominant species in fermented goat milk and fermented cow milk was Leu.mesenteroides＞L.helveticus＞Lac. lactis subsp. lactis whereas that of fermented sheep milk was L.helveticus > Leu.mesenteroides > Lac. lactis subsp. lactis.

In this paper, we review metagenomic DNA analysis techniques which are widely used to detect the microbial diversity in traditional fermented dairy products with particular focus on molecular marker technologies based on 16S rRNA gene sequences, such as denaturinggradientgel electrophoresis(DGGE), restriction fragment length polymorphism (RFLP), terminal restriction fragment length polymorphism (T-RFLP) and single-stran dconformation polymorphism(SSCP). The recent progresses in the application of these methods are summarized in detail.

In the present study, 5 strains of Streptococcus thermophilus which were isolated from traditional fermented dairy products were selected to perform fermentation experiments. During the fermentation process and 504 h of storage at 4 ℃, some indexes such as fermentation time, titratable acidity (TA), pH value and viable cell counts were determined, and the composition of organic acids was tested by reverse phase high performance liquid chromatography(RP-HPLC). Fermentation and acid-producing properties of Streptococcus thermophilus were evaluated; meanwhile changes in organic acid composition and post-acidification characteristics during storage were determined. After 2 h of fermentation at 42 ℃, the pH of fermented milk by each of the five strains declined rapidly. The fermentation reached its end-point at 5–9 h, and the shortest fermentation time was required for strains IMAU10632 and IMAU20772. Over the 504 h storage period, the pH of milks fermented by Streptococcus thermophilus was reduced by about 0.5 and finally reached a stable level of about 4.2, and acids were produced at lower rates in all fermented milks until the acidity values reached levels below 90 oT , suggesting the weak post-acidification ability of the 5 strains. Furthermore, IMAU10632 was selected from these strains, which could shorten milk coagulation time, increase acid-producing rate, enhance post-acidification ability and reach a viable cell count exceeding 108 CFU/mL which remained unchanged over the entire storage period.